Crabapple Automotive Glossary of Terms
(Terms presented under headers listed below)
• Fuel System
• Cooling System
A metal shaft that is turned by the engine, which, in turn (pun intended), rotates the wheels.
A moveable joint which is part of the steering linkage. It allows the front wheels to move, and when they go bad, you’ll notice symptoms from poor steering response, to noticeable clunking going over bumps and potholes.
Hard metal, antifriction devices which are found between two moving parts. They are often lubricated with grease.
The metal unit behind the engine that holds either the manual clutch assembly or the torque converter of an automatic transmission.
A band, usually made of rubber, that connects two pulleys thereby transferring power from one to the other. You’ll only notice these when they squeal (indicating a need to be tightened or replaced), or when they break and stuff stops working.
The combustion chamber houses thousands of literal explosions per minute, and all of these explosions can leave residue on the spark plug. The color of this residue can tell you a lot about the “quality” of that explosion, and help you verify everything is going on as it should. The buildup of carbon deposits on spark plug electrodes causing the spark plug to misfire, so cleaning and/or replacing them per OEM recommendations is important, especially if your engine seems down on power, and the plugs are due for replacement.
On manual transmissions, the clutch is a mechanical device–operated by the clutch pedal–that engages and disengages the engine from the transmission so that you can change gearsm idle without moving, etc. It generally consists of a clutch disc, a pressure plate, and a flywheel.
One of the three major components of a clutch assembly, the clutch disc is a friction place located at the end of the driveshaft, and is one of the high-wear items in the clutch setup.
The pedal next to the brake pedal that allows the driver to operate the clutch when changing gears, very brief idling, and so on. (For extended periods of idling the transmission should be placed in neutral rather than “freewheeling” the flywheel by holding the pedal down.)
This is where the magic happens. The combustion chamber is the top of the cylinder where the air/fuel mixture is compressed by the piston and ignited by the spark plug.
The squeezing of the air/fuel mixture by the upward movement of the piston (in the cylinder).
The combined parts that keep your engine from overheating while it’s housing tens of thousands of explosions per minute, mainly the radiator, any radiator fans, the thermostat, cooling hoses, and water pump.
One of multiple bores in the engine block–a V-2 having six cylinders, a V-7 eight cylinders, and so on. It houses the piston, which travels up and down in the cylinder to compress the air/fuel mixture and produce power.
The top “half” of the engine, and the part of the engine responsible for the “breathing,” the cylinder head sits on top of the engine block, and contains the engine valves, and often the camshafts as well.
A box of gears between at least two wheels that allow your engine to send power to the wheels.
A reinforced belt used to operate certain components, most notably the alternator.
A spinning metal shaft that transmits power from the transmission to the wheels via separate axles.
This is often referred to by manufacturers, especially in regards to warranty coverage. Though definitions can vary, it mainly refers to primary engine and transmission components that make the car “go.”
You car has two primary types of valves–Inlet and Exhaust–the act as little “doors” to hold air in and let air out, depending on the need. The exhaust valve opens to allow the spent combustion gases to exit the combustion chamber.
Located between the engine and radiator, the fan draws air from the radiator onto the engine in order to cool it.
A flexible rubber belt connecting the fan to the alternator and crankshaft pulley. Also called the ‘drive belt’.
The sequence the cylinders ignite or ‘fire’ in. This can be botched if the spark plug wires are not installed on the correct plugs, and without the correct firing order, your vehicle isn’t going anywhere.
Cleaning the rust and dirt buildup from an engine’s cooling system (e.g. radiator, hoses). While a qualified mechanic can handle this for you, it’s not really that difficult, and kits are available at most automotive parts stores to help you get it done.
One of the main components of your clutch assembly, a flywheel is a metal disc about the size of turkey platter (except that it’s not at all shaped like a turkey platter, being as that it’s round and not oval, so maybe that’s just confusing) that provides “momentum” to move the car from a stop.
A vehicle that is driven by its front wheels, as opposed to the rear. Most popular sedans, minivans, and other people-movers are front-wheel drive because it is simpler, provides superior traction in rain or snow, and is generally thought to be somewhat “safer” than rear-wheel drive for the reasons.
A housing containing gears, such as a transmission. Gearbox just sounds cooler, doesn’t it?
The part of the engine sitting on top of the engine block, the head contains the engine valves.
The gasket between the head and the engine block. When these leak, they allow oil and coolant to mix, and things go bad in a hurry.
A sound that occurs when the air/fuel mixture is igniting too soon. It is usually caused by a poorly timed engine, the use of low octane gas, or the build-up of carbon deposits on the piston tops. If your engine is “knocking,” whether through repair or the use of higher octane fuel, it needs to be addressed immediately. (Yes, this is classified as a funny noise.)
Any system that stores, cools, cleans, and circulates oil throughout an engine.
A transmission system in which the gears are operated by the driver by means of a stick shift and clutch pedal. Manual transmissions are generally preferred for high-performance driving, or as a lower-cost alternative to more expensive automatic transmissions. They are also simpler, and less costly to repair as well.
Rubber covered brackets that hold the engine to the frame. Typically these do not fail, though worn mounts can allow the engine to move excessively in the engine bay and cause other issues.
These are the most often replaced items on a car, so get familiar with them. As the name implies, they simply filter the engine’s oil, and being as oil is the lifeblood of any engine, their job is crucial. Oil filters should be replaced with every single oil change–and you should strongly consider OEM-specific oil filters as well. It is a good idea to buy these in bulk if you change your own oil–with crush washers, of course.
A chamber at the bottom of the crankcase that stores oil. Every notice that hot, sizzling, dripping sound when you turn your vehicle off after a drive? That is oil dripping down into the hot oil pan.
A pump located inside the engine that circulates oil from the oil pan to the moving parts of the engine. These rarely fail, and if they do, usually means your engine is toast. Clean, fresh oil makes for a happy oil pump.
An optional gear that allows the drive wheels to turn faster than the engine. It allows for better fuel efficiency during high speed highway driving.
A lever extending from the steering gear to which steering linkage is attached.
A steering system using hydraulic power to ease steering, almost all modern vehicles feature power steering, though many lighter performance cars don’t because not only is power steering not always necessary, but it can also ruin the “feel” and general feedback between the tires and the driver.
One of the major components of the clutch assembly, the pressure plate is forced by springs against the clutch disc which then causes the engine’s power to be transmitted to the various gears of a manual transmission.
Rack & Pinion
A steering system in which a round pinion gear turns against teeth cut out of a flat rack.
A shaft on which the wheels and wheel bearing mount.
A type of ball joint located at the end of each tie rod.
A system that connects the steering wheel to the front wheels thus allowing the vehicle to be steered.
Slang for a car with a manual transmission, a “stick shift” is also a gearshift located on the floor between the front seats.
On manual transmission cars (“stick shifts”), a synchromesh is s device that causes two gears to spin at the same rate thus allowing them to mesh smoothly. If yours are bad, your transmission won’t shift smoothly, and may even refuse to go into gear.
The part of the clutch, activated by the clutch pedal, that allows the clutch to disengage. Sometimes when they’re noisy, you can hear a cricket-like chirping come and go as you *just* press in the clutch pedal.
The linkage between the steering rack and knuckle arm.
Tie Rod Ends
Grease fittings or ball joints on the ends of the tie rods.
The coordination of the valves, pistons, and spark. The timing must be exact or engine performance will suffer.
A rubber/fabric belt that drives the camshaft by linking it to the crankshaft. It assures that the valves will open and close at the proper time for efficient ignition. This is an important maintenance item, as when neglected, it can break, which will at best, make the engine stop dead in its tracks, and at worst cause the pistons and the valves to collide (depending on whether you have an “interference” engine or not). Replace these per manufacturer recommendation.
Some manufacturers use timing chains instead of timing belts–many Nissan models, for example. A timing chain is basically a metal chain that drives the camshaft by linking it to the crankshaft. It assures that the valves will open and close at the proper time for efficient ignition.
A braking system that keeps the wheels from locking up during aggressive stopping. Though anti-lock brakes will often shorten stopping distances, their main advantage over non anti-lock systems is their ability to provide the driver will full steering control during full-force stops. A car with locked wheels will not steer!
Brakes work by hydraulic pressure, which is extraordinarily powerful–provided no air makes its way into the fluid. Bleeding the brakes simply means to “push” the air bubbles out of the fluid so your brakes actually work when you press the brake pedal!
Brake Backing Plate
A metal plate inside the brake drum on which the brake shoes, wheel cylinder, and other brake parts are mounted.
The little fruitcake-sized and -shaped metal devices on disc brakes that you can see through the wheel. They house the brake pads, and their job is to squeeze the pads onto the discs when you hit the brakes so that your vehicle stops.
On a drum braking system a small cylinder that uses brake fluid to exert hydraulic pressure which forces the brake shoes against the brake drums and stops the vehicle.
On a drum braking system these are metal drums that are mounted on each wheel. The brake shoes press against the inner surface of the brake drum and cause the vehicle to slow down.
A special fluid used in a hydraulic brake system. Always use fluids that meets or exceeds OEM recommendations (recommendations that you can find in your owner’s manual). Brake fluids are rated in DOT levels, the higher the DOT rating, the more resistant the fluid generally is to boiling (which is at least as bad as it sounds).
Thin little metal tubes that allow the brake fluid pressure move from the master cylinder to the brake calipers, which in turn squeeze the brake pads onto the brake discs.
On a drum braking system brake lining is a high-friction material that is attached to the brake shoes.
On a drum braking system brake shows are curved pieces of metal with brake lining attached. When pressed against the inside surface of the brake drums, they cause a vehicle to stop.
Type of brakes that work by squeezing brake pads against a disc–thus “disc brakes.” Most modern cars use this type of braking system.
Most automotive braking system are operated by either discs or drums. Drum brakes are rare on modern vehicles, and are used only as a low-budget or simpler alternative. Drum brakes work by pressing brake shoes against the inside of the brake drum to make a vehicle stop, and their existence on your car, if nothing else, should make you feel old-school-cool in a Redd Foxx/velvet drapes sort of way.
Fluids can’t readily be compressed. Hydraulic systems use that resistance to being compressed to generate force to operate things like brakes, as they can provide tremendous force.
A device that stores brake fluid and hydraulically forces it through the brake system.
A device that uses engine vacuum to assist in braking.
A brake system that uses a power booster to ease braking, almost all modern vehicles feature power brakes.
This is what is sounds like–springs a little longer than a loaf of bread that sit at all four corners of most vehicles to absorb and absorb road irregularities and dissipate their energy by (slightly) bouncing.
This one is exactly what it sounds like: an actual filter that removes dust and dirt particles from the air stream being ingested by the engine.
This is what is sounds like it’d be–the mix of gasoline and air that allows your engine to produced power. There is an ideal ratio of air to fuel that is most conducive to a complete burn of the gasoline, which is 14.6 parts air to 1 part air, also known as the “stoichiometric ratio.” (I challenge you to work that into a sentence sometime in the next 6 days without the person you’re talking to noticing.)
A canister that is filled with charcoal and is used as an emissions control device to keep the oceans blue and the grass green.
On carbureted engines, this device ingests and mixes the gas and air so that it may be “fed” to the engine.
This is like an air filter in your exhaust system, only this “filtering” is done chemically by taking advantage of the extremely high exhaust temperatures. These can go “bad” if your air-fuel mixture gets way out of whack, acting like a cork in the exhaust. Like so many other automotive parts, catalytic converters are really only noticeable when they stop working properly.
Another initialism (an automotive industry favorite), the EGR stands for Exhaust Gas Recirculation, an emission control device that helps make the ocean and skies blue and the grass green by recirculating some of the exhaust gases back into the engine for another burning.
Emissions are basically chemicals in exhaust gases that are harmful to air quality, mainly carbon monixide (CO), hydrocarbons (HC), and nitrogen oxides (NO). Healthy engines produce fewer of emissions, and older or “unhealthy” engines produce more. Some engine designs–like rotary engines, for example–produce more of certain emissions than others.
The gases that result after the air/fuel mixture has been burned in the engine’s combustion chambers. Vehicle emissions are contained within the exhaust gases.
A set of pipes, one for each cylinder, that carry exhaust gases from the combustion chambers to the exhaust system. These can crack in some designs, producing a “ticking” sound near the manifold while the engine is running, but generally are a non-wear item.
A series of metal tubes from the engine cylinder head to the tip of the muffler that carry the burned gases from the engine’s cylinders to the–*gulp*–atmosphere.
This not-good situation most often occurs in carbureted cars whose engines are injected with too much fuel to start and/or run properly.
A mist-like vapor of gasoline and air. Like with pepper and exercise, the right amount is good, but too much of one can ruin things in a hurry. (Recall our definitions: Lean means too much air, Rich means too much fuel. This stuff has to be precise or fuel efficiency and performance suffer!)
Usually hard to find in the engine bay, and about the size of a can of your favorite cola, the fuel filter’s job is to–you guessed it, filter the fuel, removing dirt, grit, and other nasty stuff that could clog your other parts of your fuel system. These should be changed per manufacturer recommendation, and while doing this jod yourself isn’t difficult, anytime you mess with fuel system components, the margin for error is much smaller. When things get hot, fuel is a dangerous thing.
Most modern engines have their fuel supplied to them by a fuel-injection system, as opposed to the older, dated design of carbureted fuel systems. Fuel-injected engines are more efficient, as they are able to control the fuel more precisely.
Fuel injectors are little nozzles about the size of a lighter that squirt gas into the combustion chambers. You have one injector per cylinder, and they generally do not have to be replaced as a wear item unless they have failed. Some engines, like older VQ-series engines in early Nissan Maximas, are known to have higher injector failure rates than others.
A pump that draws gasoline from the fuel tank to either the carburetor or fuel injectors. While these can fail slowly, typically they work or they don’t. Changing them is also no fun, as they are usually located in the fuel tank. Good times right there.
A set of pipes, one for each cylinder, that carry the air/fuel mixture to the cylinders.
Lean Fuel Mixture
An air/fuel mixture that contains an excessive amount of air in proportion to gasoline. This leads to higher exhaust gas temperatures, and is generally more dangerous to the health of your engine than an overly-rich mixture, though neither are desirable.
The failure of the air/fuel mixture in one or more cylinders to ignite while the engine is running.
A sound that occurs when the air/fuel mixture is igniting too soon usually caused by a poorly timed engine or the use of a low octane gas. Pinging is a symptom of a dangerous condition in the combustion chambers, and should not be ignored on any engine you car about.
A phenomenon in which the air/fuel mixture self-ignites before the spark plug fires. This generally results in a knocking or pinging sound.
Rich Fuel Mixture
There is an ideal mix of air and fuel. Too much air causes a “lean” condition, while too much fuel produces a “rich” condition. Most vehicle’s are “rich” from the factory because it is generally safer than a lean condition (lean conditions yield high exhaust gas temperatures that can damage other parts, and are unsafe). A “little” rich is common; overly-rich is not good, and some symptoms of a rich mixture include excessive soot on the exhaust tip, and a noticeable drop in fuel efficiency.
The part of the fuel system that houses the throttle, it is often tied directly to the throttle control/pas pedal, so that as you press down the gas pedal, a little valve in the throttle body opens up and allows the vacuum of the engine to ingest air and start to party.
Air Flow Sensor
This is a sensor on a fuel-injected car that measures the amount of air entering the throttle body. This measurement is then used by your car’s ECU to maintain proper air/fuel mixture.
A belt-driven, saucer-sized device which uses the engine’s power to generate electrical energy.
A device which stores electrical energy, and is continuously charged by the alternator. Its primary purpose is to provide power to start an engine.
The two metal posts which protrude off the top or side is the battery. One terminal is positive, the other negative. These should be clean to allow the battery to function properly, though care must be taken when cleaning the “crust” from the posts, as it is usually acidic and dangerous.
A system which uses a fan belt driven by the engine to enable the alternator to create electrical energy which is then stored in the battery.
This important little guy amplifies a small amount of electrical current and sends it to the spark plugs by way of the distributor, making it a critical part of the ignition system.
The part of the ignition system that distributes the current to the spark plugs. These typically do not “wear”–they either work, or they don’t.
A literal cap that covers the distributor and helps distribute electricity to the spark plugs via spark plug wires. This is a “wear” item that is often replaced as part of a “tune-up.”
Unless some sort of electrical problems “ruins” yours, your ECM is typically one of those it-either-works-or-it-doesn’t items. Also referred to as the ECU, the “ECM” initialism refers to the Engine Control Module, the “computer” that operates various automotive components (depending on the manufacturer).
A modern ignition system that transmits current to the spark plugs by highly precise electronic means. It eliminates the need for a condenser and points.
Different manufacturers refer to these on-board “computers” by unique initialisms–ECM, ECU, etc.–but fundamentally most are the same: they use inputs from various engine sensors to control the engine’s operation.
Sometimes called the “earth,” without a ground your electrical system cannot function. The negative terminal of your battery is a type of ground, as are the various wires you may see in your engine bay that are bolted only to bare metal in the engine bay or fender, but seem to have no other function. That is probably a ground, and when these are broken, disconnected, or otherwise fail, they can make other systems in your car start acting funny–funny in a bad way.
The part of the ignition system which amplifies a small amount of current and sends it to the spark plugs by way of something called the ‘distributor’. These can fail, but are generally some of the sturdier items in the ignition system.
A system of electrical parts meant to provide the spark to the spark plugs, that in turn ignite the air/fuel mixture in the combustion chambers.
The piston moves up and down in the cylinder (unless you’ve got a flat “boxer” engine, in which case it moves horizontally) to compress the air/fuel mixture, which is then sparked by the–you guessed it, spark plug. The timing of that spark is critical; too soon or too late, and things stop working correctly, and in some cases bending and breaking.
A wire with thick rubber insulation that carries the high voltage current from the ignition coil to the spark plug.
A sensor which detects engine knock or ‘ping’ and then transmits a signal to the engine’s computer. Too much knock can break these sensors, which have to then be replaced.
A sensor that detects the load an engine is under. It sends its reading/signal to the engine’s computer so that it can properly calculate how much fuel needs to be injected.
Mass Airflow Sensor
A sensor which measures the amount of air entering the engine. It sends its readings to the engine’s computer.
The battery terminal that conducts electric current back to the battery on cars with negative ground. It is always marked with a’-‘ as opposed to the positive terminal ‘+’.
A dashboard light that illuminates the oil pressure drops below a certain level. Don’t wait for the oil light to tell you what your oil level is though. Check it on some sort of a schedule–monthly at minimum, and more frequently if your vehicle is known to burn or leak oil.
A circuit that is interrupted, such as by an open switch, a bad connection, or an internal break. Generally not a positive thing as far as your vehicle is concerned.
The bane of owners with “check engine” lights everywhere, the oxygen sensor is a device that can fail with frustrating frequency. This device measures the oxygen level in the exhaust gases, allowing the engine to adjust the air/fuel mixture accordingly. However, each manufacturer uses the oxygen sensor differently–and uses oxygen sensors of varying qualities and design as well, so that a failing oxygen sensor in one car may produce no noticeable affects, while in other cars a failed oxygen sensor (also called an “oh-two sensor” for the chemical descriptor) can radically impact fuel efficiency and overall engine performance–in some cases, the car may not even run. If you’re going through oxygen sensors like nobody’s business, it’s probably a symptom of larger problem, often having to do with an “off” air/fuel mixture damaging the sensor.
Part of the Positive Crankcase Ventilation system used mainly on older vehicles. When this valve is open, it sucks unburned fuel vapor from the crankcase to the intake manifold for a second burning, and helps lower emissions. Replacing them is inexpensive, and a good idea on older vehicles whose PCV valve is older or of unknown age.
The battery terminal that leads to the starter. It is usually marked with ‘+’ or ‘pos’.
As in to recharge a battery, which means to restore its dissipated electrical energy.
A switch that allows a small current in one circuit to control a greater flow of current in another circuit.
Measured in ohms, and an assessment of a circuit’s resistance to “promote” electricity, the resistance of many automotive parts that operate electrically and electronically can help you assess that part’s general health. If resistance is too low or too high, it is generally “broken,” or otherwise out of specification.
A device that restricts the flow of current in a circuit.
A plastic device that sits atop the distributor shaft and conducts electric current to each spark plug terminal.
A device which measures some engine factor and transmits a signal (i.e. reading) to the engine’s computer, many of whose function can be tested with an ohmmeter.
The adjustment of the ignition timing so the spark plugs fire sooner than they have previously been firing.
A sound that occurs when the air/fuel mixture is igniting too soonand is very often caused by a poorly timed engine.
Along with oil and oil filters, spark plugs are the face of automotive maintenance, devices that produce an electrical spark to the combustion chamber in order to ignite the air/fuel mixture. (Your lawnmower probably has one too, if that interests you.) Replace these per your manufacturer recommendations, though you can replace them sooner if you have a condition in the combustion chamber that keeps ruining the plugs. In fact, in many ways the spark plugs (along with fuel efficiency) can be considered a window into the health of your engine, and can be removed and inspected to have a look-see into what’s going on in the combustion chamber.
Spark Plug Cable
A wire with thick rubber insulation that carries the high voltage current from the ignition coil to the spark plug.
Spark Plug Gap
The distance between the center and side spark plug electrodes across which the spark must jump.
Spark Plug Wire
A wire with thick rubber insulation that carries the high voltage current from the ignition coil to the spark plug.
The adjustment of the ignition timing so the spark plugs fire later than they have previously been firing.
An electrical motor that causes the engine’s crankshaft to begin turning, which starts the engine running.
The solenoid/switch used in the string system. It is typically built into the starter motor.
Cooling Systems (Thermostat, Radiator)
The workhorse of your cooling system, the radiator is a device that keeps the engine at proper operating temperature by passing coolant through a series of water channels that allow heat to be released.
The thermostat is like a gate that remains shut until the coolant reaches a set temperature, at which point it opens and lets coolant pass. Its basic function is to allow the engine to warm more quickly.
Little rubber or polyurethane linings that cushion noise, friction, and movement. Typically found in suspension systems, stiffer bushings can often be installed for increased steering feel and performance applications. Worn bushings will often produce “sloppy” handling and excessive clunking and play in steering system.
The chassis can be thought of as the underbody structure of the car. The engine and body are mounted in and on the chassis.
Suspension pieces that allow the wheel to move freely–whether through bumps or change of direction.
Another part you may only see or hear about when it goes bad, the CV joints are flexible couplings between two shafts that allow each shaft to keep the same driving speed regardless of angle.
An old-school type of suspension design rarely used in modern automotive manufacturing, leaf springs are a series of stacked, metal plates that bend flexibly to absorb the bumps and shocks of driving.
Along with the suspension spring, the shock (many manufacturers such as BMW and Toyota often use a Macpherson strut design that has the same function) and suspension arms and links, the shock is one of the major components of a vehicles suspension. Its basic function is to control the spring, which would otherwise bounce your vehicle like a pogo-stick after bumps. Shocks are definitely “wear” items, and should be replaced per your manufacturer’s recommendations. If you notice your car’s ride a bit bouncy, consider new shocks all around.
A system of parts–suspension arms, springs, and shocks–that cushions a vehicle from the bumps and irregularities of the road, resulting in a smoother ride.
Additives are substances added to such products as coolant and engine oil so as to enable them to perform better, last longer, and provide secondary benefits.
A liquid solution which, when mixed with water, raises the boiling point and lowers the freezing point of water. It is poured into the radiator.
Extremely thick lubrication oil that is used to lubricate the steering and suspension systems.
The greasing of the steering system, suspension system, and drivetrain. A lube job can be necessary to keep moving parts that touch from wearing each other down, but can also be “oversold” by repair shops. If your vehicle isn’t having squeaking/clunking issues in the suspension–which a lube job may or may not repair–stick to your manufacturer’s recommendations for such maintenance tasks.
Replacement of the high-wear items like ignition components (spark plugs and wires), air filters, fuel filters, etc.
The process of rebuilding or replacing all of the major components of an old, tired engine. It can be much cheaper than a new car, but it should be done by a mechanic who is truly qualified, lest your vehicle turns into a money pit.